feat(spawn): share host spawn-pi mesh + models.json with spawned containers

- bind $LVMH_HOST_PI_RUNTIME_DIR/spawn-pi -> /root/.pi/spawn-pi (rw) so
  container pi's join the host pi's node mesh (spawn_pi/list_pi_nodes/
  send_pi_message now reach across the host/container boundary)
- bind host models.json (when present) over the stale image-baked
  fallback so newly added catalog models resolve in spawns

docker-compose.yml

@@ -19,6 +19,9 @@ services:
       # docker.sock bind semantics: bind sources resolve on the HOST, so
       # this must be the HOST path of the pi config (auth.json etc.).
       LVMH_HOST_PI_AGENT_DIR: ${LVMH_PI_AGENT_DIR:-/home/alarm/.dotfiles/pi/agent}
+      # host pi runtime dir (spawn-pi mesh: nodes + sockets), shared rw with
+      # spawned containers so host pi and container pi's form one mesh
+      LVMH_HOST_PI_RUNTIME_DIR: ${LVMH_PI_RUNTIME_DIR:-/home/alarm/.pi}
       LVMH_SECRETS_DIR: /zdata/root/lvmh-secrets
       LVMH_CLOAK_CACHE_DIR: /home/alarm/.cloakbrowser
       LVMH_PLAYWRIGHT_CACHE_DIR: /home/alarm/.cache/ms-playwright